1. Field of the Invention
This invention relates generally to a wireless digital communications system and control of a wireless network having battery operated communication devices.
2. Description of Related Art
Short-range wireless networks consist of communication devices such as portable media players, personal communication devices such as mobile phones, digital monitoring devices, etc. These communication devices are generally configured in networks structured as a star network or a mesh network. In a star network, a central computer or hub controls the communication between the communication devices connected to the remote nodes of the star. In a mesh network, each communication device is communicates with any or all of the other communication devices in the network. Each communication device can act a router of information between the communication devices.
Typically, the networks comply with network protocols defined in specifications such as Bluetooth or the IEEE 802.11. These specifications provide: Data formats for data exchange; Address formats for data exchange; Address mapping; Routing; Detection of transmission errors; Acknowledgements of correct reception of packets; Loss of information—timeouts and retries; Sequence control; Flow control; and syntax and semantics of the communications. Further, these protocols employ spread spectrum frequency hopping techniques for transmitting the data to provide secure communications by increasing resistance to natural interference and collisions with other transmitters within the reception area. Synchronization to the hopping sequence is required for communication devices to be able to transmit and receive the communicated between them. It has always been a challenge to achieve fast synchronization while keeping the power consumption low for wireless system protocols. All existing frequency hopping standard protocols such as used by Bluetooth and IEEE802.11, do not achieve this very well. In the case of Bluetooth, low-power is achieved at the expense of very long acquisition time very often in the order of seconds in practice. For 802.11, power consumption is always high to allow synchronization to be much faster than Bluetooth.
The ISM (industrial, scientific and medical) radio bands were originally reserved internationally for the use of RF energy for industrial, scientific and medical purposes other than communications, such as radio-frequency process heating, microwave ovens, and medical diathermy machines. The powerful emissions of these devices can create electromagnetic interference and disrupt radio communication using the same frequency, so these devices were limited to certain bands of frequencies. In general, any communications equipment operating in these bands must accept any interference generated by ISM equipment. For interference avoidance in the 2.4 GHz ISM band, Bluetooth has a very complex adaptive hopping scheme that constructs a channel list to which the system would hop. This requires a large amount of overhead in communicating the information, as well as creating and maintaining the list, leading to further power consumption.
A further problem exists with the portable devices operating in the 2.4 Ghz ISM band. These wireless devices lose their connectivity once out of range. Wide-area networks such as GSM (Global System for Mobile Communications) or other cellular systems are not power efficient enough to support battery life for months and therefore is not suitable for communication devices such as portable and/or wearable health management systems.